Grey map tiles, you’re not the first one. There are many many people with issues, and it’s usually due to a draw that has already taken place before the view was rendered. I.e., don’t resize your map inside an init function, it doesn’t make sense. You only should initialize the map once on the first time you’re viewing it. Any alterations should be seperated from the initialization, as does the resize event.
Thus the resize event should occur after your map has initialized, always. Not in the process itself.
Maybe you have an error on the device? Did you already debug it on a device with the inspector open?